The corticospinal tract (CST) is essential for voluntary control of the body's distal musculature. The absence of effective treatments to restore this pathway after injury has devastating consequences for victims of spinal cord damage. In animal studies, progress has been made in getting injured CST axons to regenerate by altering the extracellular environment, though to date, the number of fibers that grow past an injury site remains small. Recent experiments in our lab show that the purine nucleoside inosine activates an intracellular mechanism in neurons that leads to extensive axon growth. In mature rats with unilateral transections of the corticospinal tract, inosine infused into the normal sensorimotor, cortex induced uninjured cortical pyramidal cells to sprout axon collaterals that crossed over to the denervated half of the spinal cord, and in some instances formed anatomically appropriate synapses. Following up on these observations, Aim 1 will examine whether transected corticospinal tract axons can be induced to regenerate by treating their cell bodies with inosine, while at the same time using neural stem cells and/or olfactory ensheathing cells to provide a cellular environment at the lesion site conducive to axonal growth. In Aim 2 we will retrogradely label the pyramidal cells of the rat's sensorimotor cortex prior to surgery and then, after various experimental treatments, use fluorescence-activated cell sorting to isolate the neurons that give rise to the corticospinal tract. Through the use of microarrays (gene chips), we will identify genes associated with axon growth, growth cone guidance, and other aspects of corticospinal tract regeneration. These studies will provide basic information on the biological mechanisms that regulate CST axon growth and will help us develop novel approaches to restoring, function after injury to this pathway.